Thermoforming machines are used to generate a container from a sheet. These machines comprise an upper tool and a lower tool with a specific configuration, cooperating with one another to shape a sheet and thus generate a container. The sheet is arranged between both tools and is deformed when the tools move close to one another, taking the shape of the tools, corresponding with the desired shape of the container. This function is referred to as forming, and the machine comprises a forming station where the tools are arranged and where the sheet is deformed to obtain the desired end container.
The machine can further comprise a sealing station with other tools also cooperating with one another, where an upper sheet or cover is sealed to the previously formed container with the product already in it. As in the forming station, the design of the tools of the sealing station also depends on the shape of the container, but these tools can be different from the tools of the forming station because their function is to seal the container previously generated in the forming station.
If a container having a different shape is to be generated, the tools have to be replaced with other tools with the suitable configuration, both in the forming station and in the sealing station, an operation known as a format change.
Document EP 2383091 A1 belonging to the present assignee discloses a packaging machine comprising a tool change system, whereby a lower tool of the machine can be replaced in a fast and simple manner.
Various ways to change the format, in which the lower tool and the lower tool are changed separately in order to make the format change, are known of the state of the art, such as those which are disclosed in documents EP 2052979 A1, EP 1234765 A1 and EP 2380811 A1.
Document EP 2052979 A1 discloses a format change where the lower tool is changed by removing it from the corresponding station of a packaging machine below the sheet. In another additional operation, the upper tool is changed by removing it from the corresponding station of a packaging machine above the sheet. For this last task, a cover is released and removed from a mechanism where the upper tool is arranged, and the upper tool is removed from the mechanism through the free space that is left when the cover is removed. This way of changing the format further allows not having to cut and move the sheet(s).
Document EP 1234765 A1 discloses a machine with a first transfer store for replacing the lower tool and a second transfer store for replacing the upper tool, each tool being replaced separately. The first transfer store is arranged below the sheet and the second transfer store is arranged above the sheet, such that they do not affect the sheet.
Document EP 2380811 A1 discloses a packaging machine with a forming station and a sealing station in which an upper tool and a lower tool cooperating with one another act to generate a container and to seal the container, respectively. In at least one of the stations the machine comprises a first transfer store arranged below the sheet for the lower tool and a second transfer store arranged above the sheet for the upper tool, each tool being replaced separately.
This way of changing the format, by changing the lower tool and the lower tool separately, can have the advantage, at least in some cases, of facilitating the work of the operator (or operators) responsible for making the change, but in contrast it can involve a long format change time because two independent changes (two tasks) are required, which can be prejudicial in production terms, and therefore in financial terms.
Document WO 2011104036 A2 discloses a format change method for a packaging machine in which a lower tool and an upper tool of the machine are changed. Both tools are replaced above the machine, so they are lifted by means of an actuator to a position above the machine where an operator can replace them with other tools, which are subsequently introduced again in the machine by lowering them. For the format change, the two tools are decoupled, respectively, from a lower part and from an upper securing block of the forming station to which they are coupled during normal operative or operational working of the machine, and the securing block of the forming station moves in order to be able to move the tools in a vertical direction until arranging them above the machine.